A controller or a programmable logic controller (PLC) system known in the art may control a control target device by executing a task including a user program in every predetermined period to calculate an output signal based on an external input signal and output the signal. The controller may have the function (trace function) of tracing temporal changes in an input signal and an output signal (input and output signals).
For example, Patent Literature 1 describes a controller that collects variables referred to and updated by a user program during execution of a task including the user program.